The notion of stability is central to the definition of personality traits, which are generally thought of as enduring tendencies or habitual patterns of behavior, thoughts, and emotions (McCrae &Costa, 2003), but stability does not imply immutability. Under normal circumstances, adult traits are largely stable, as indicated by high correlation coefficients computed for a group assessed twice on the same trait. These coefficients represent the average stability for a sample, but individuals vary in terms of their intra-individual stability. Recently, a longitudinal intra-individual approach was used to examine stabilities across two successive intervals traced within individuals. Individual stability coefficients from three sequential assessments were computed to evaluate intra-individual (i.e., within-person) change in stability over time. For both trait and profile (ipsative) stability, results indicate that intra-individual stability increases up to age 30 and then plateaus. Neither demographic variables (sex, ethnicity, education, and secular trends), nor the standing on the five major dimensions of personality, were predictors of change in trait stability. Contrary to results from studies of adolescents, personality maturity was unrelated to personality stability in adulthood. These findings support the notion that personality stability plateaus early in adulthood. Despite the relative stability of individual differences, in recent years we have extended the studies of mean-level change in personality by examining longitudinal trajectories in more diverse samples and cross-sectional trends across cultures. We have also focused on community or epidemiological investigations to study the causes of the modest changes that occur in personality traits in adulthood. In addition to health (see below), we are interested in the reciprocal influences of personality and life circumstances, such as job characteristics and retirement transition. Furthermore, we aim to delineate the neural and cognitive correlates of personality dimensions across longitudinal assessments. In health-related research, we have examined the association between personality traits and several biomarkers of mental and physical health. Below are some examples of this research. Brain derived neurotrophic factor (BDNF) is among the most promising biomarkers of mood disorders. BDNF regulates synaptic plasticity and neurogenesis, and BDNF plasma and serum levels have been associated with depression and other psychiatric and neurodegenerative disorders. In clinical samples, circulating levels of BDNF are reported to be lower in depressed patients compared to controls and are reported to increase significantly with antidepressant treatment. In large community-based samples, we have examined whether BDNF concentration in plasma and serum are associated with the personality trait of Neuroticism, a major risk-factor for depression. We have found that serum but not plasma BDNF is associated with measures of psychological distress (Neuroticism, depressive symptoms). Among the markers of physical health, we have examined the association between personality traits and obesity, dyslipedemia, metabolic syndrome, arterial thickening, walking speed, muscle strength and inflammation. Below are summaries from one study on obesity and one on an inflammatory marker. Personality traits contribute to health outcomes, in part through their association with major controllable risk factors, such as obesity. Body weight, in turn, reflects our behaviors and lifestyle and contributes to the way we perceive ourselves and others. Based on data from a large (N = 1,988) longitudinal study that spanned more than 50 years, we examined how personality traits are associated with multiple measures of adiposity and with fluctuations in body mass index (BMI). Using 14,531 anthropometric assessments, we modeled the trajectory of BMI across adulthood and tested whether personality predicted its rate of change. Measured concurrently, participants higher on Neuroticism or Extraversion or lower on Conscientiousness had higher BMI;these associations replicated across body fat, waist, and hip circumference. The strongest association was found for the impulsivity facet: Participants who scored in the top 10% of impulsivity weighed, on average, 11Kg more than those in the bottom 10%. Longitudinally, high Neuroticism and low Conscientiousness, and the facets of these traits related to difficulty with impulse control, were associated with weight fluctuations, measured as the variability in weight over time. Finally, low Agreeableness and impulsivity-related traits predicted a greater increase in BMI across the adult life span. BMI was mostly unrelated to change in personality traits. Personality traits are defined by cognitive, emotional, and behavioral patterns that likely contribute to unhealthy weight and difficulties with weight management. Such associations may elucidate the role of personality traits in disease progression and may help to design more effective interventions Another example of this research is a study on Interleukin-6 (IL-6), a peripheral marker of chronic inflammation that increases with age and is implicated in a wide range of health outcomes. Although beneficial in response to acute injuries, chronic production of IL-6 leads to increased morbidity and mortality. Higher levels of IL-6 are associated with frailty and disability among the elderly, and elevated IL-6 has been linked to numerous chronic conditions, such as diabetes, osteoporosis, and cardiovascular disease. A population-based sample (N=4,923) from four towns in Sardinia, Italy, had their levels of IL-6 measured and completed a comprehensive personality questionnaire, the NEO-PI-R. Analyses controlled for factors known to have an effect on IL-6: age, sex, smoking, weight, aspirin use, and disease burden. High Neuroticism and low Conscientiousness were both associated with higher levels of IL-6. The findings remained significant after controlling for the relevant covariates. Similar results were found for C-reactive protein, a related marker of chronic inflammation. Further, smoking and weight partially mediated the association between impulsivity-related traits and higher IL-6 levels. Finally, logistic regressions revealed that participants either in the top 10% of the distribution of Neuroticism or the bottom 10% of Conscientiousness had an approximately 40% greater risk of exceeding clinically-relevant thresholds of IL-6. Consistent with the literature on personality and self-reported health, individuals high on Neuroticism or low on Conscientiousness show elevated levels of this inflammatory cytokine. Identifying critical medical biomarkers associated with personality may help to elucidate the physiological mechanisms responsible for the observed connections between personality traits and physical health.